MADRID, Spain (CNN) -- Moroccan police have arrested a prime suspect in the Madrid train bombings of 2004 but he is unlikely to be extradited to Spain, a Spanish judicial source told CNN Monday.

Instead, he is likely to be tried in Morocco, because there is no extradition agreement between the two countries.

The suspect, Abdelilah Hriz, was arrested Sunday in his native Morocco, and Spanish authorities were informed Monday, the source said.

About a dozen suspected Islamic extremists were convicted in October in Madrid for their roles in the train bombings that killed 191 people and wounded more than 1,800 on March 11, 2004.

But authorities have long said a few suspects in the attack remained at large.

Spain, since 2005, has sought Hriz, who is around 30, for suspected membership in an Islamic terrorist group, but in February, the judge who led the investigation into the train bombings added the charge of mass murder against him.

That came after DNA tests indicated Hriz was present at key locations associated with the bombings, including a rural lodging east of Madrid where authorities say the bombs were assembled, according to a copy of the judge's order viewed last year by CNN.

"The facts allow the consideration of Abdelilah Hriz as one of the alleged participants in the terrorist attacks of March 11, 2004," the judge, Juan del Olmo, wrote in that court order.

Hriz is wanted for murder in connection with the 191 people who died, attempted murder in connection with the 1,800 wounded, and causing terrorist damage to the four morning rush-hour trains ripped apart by the bombs, the judge's order said.

Early last year, Hriz was in jail in Morocco on other charges but he was later released. He has now been arrested at Spain's request in the bombings, the source said.

But because there is no extradition agreement, there is very little chance Morocco would permit him to stand trial in Madrid, the source said.

Instead, Spain is likely to send the evidence against Hriz to Morocco, the source said, and he would be expected to stand trial in that country.E-mail to a friend